This invention generally relates to fiber production and more particularly to a method and apparatus for producing large diameter spun filaments.
In the manufacture of synthetic fiber filaments, it is generally recognized that filament size is a function of a "drawing" operation wherein a continuous spun strand is submitted to a battery of equipment especially designed to "finish" the filament according to a predetermined specification. The filaments may therefore be spun and spooled for future drawing or may be spun-drawn to effect particular characteristics to the filamentary material. The "drawing" operation is known and understood by persons knowledgeable in the art and is therefore considered beyond the scope of the instant invention.
Prior to drawing, the molten polymer is conventionally "pumped" through an orifice at a substantially constant pressure in a vertically oriented spinnerette and air-quenched in a vertical cooling unit or water-quenched in a horizontal water bath. For spun filaments of the larger sizes (5-30 mil) threadline stability is insufficient for vertical air-cooling inasmuch as "necking down" of the molten polymer occurs at the orifice exit. This natural drawing or necking down of the polymer is difficult to control and therefore it is not the practice to air-quench filaments of this larger size. In this circumstance, water-quenching becomes necessary but the throughput for this cooling process is low, thus increasing the expense of producing the larger sizes.
Filaments having drawn or "finished" diameters in excess of 3-mils have become attractive for various applications and it is desirable, therefore, to produce them economically. Inasmuch as liquid cooling decreases production throughput, it would seem ideal if larger size filaments could be air-cooled since high threadline speeds could be achieved. In conventional cross flow air-cooling processes, multi-filament spinning has a tendency to fuse filaments while mono-filament spinning lacks threadline stability. Thus, problems exist in the state of the art where larger sizes are being considered.
The present invention applies a technique of electrostatic cooling that is described in the publication "Electronic Design", volume 19, No. 20, of Sept. 20, 1971, entitled "High Voltage Ionic Discharges Provide Silent Efficient Cooling". According to this technique, a high voltage ionic discharge cools a hot surface by producing a turbulence that disturbs the thin boundary layer of air molecules on the surface. These air molecules act as an insulating barrier against further cooling of the surface and thus decrease cooling efficiency.
In this respect, therefore, the present invention comprises a method and apparatus for bombarding a molten polymer filament with accelerated electrons in the presence of forced air-cooling to substantially increase the rate of cooling and allow for the formation of larger filament diameters in the spinning process. More specifically, the invention comprises a collar configuration that is mounted proximate to a conventional extruder spinnerette orifice to effect electrostatic cooling of the molten filament as it exits from the spinnerette.
The features and advantages of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals.